Wireless transmission system



Sept-'1, 1936. G. w. WALTON WIRELESS TRANSMISSION SYSTEM Filed April 12,1933 Patented Sept. 1, 1936 UETE STTES WIRELESS TRANSMISSION SYSTEMGeorge William Walton, London, England Application April 12, 1933,Serial No. 665,818 In Great Britain April 23, 1932 3 Claims.

This invention relates to wireless transmission systems and has for itsobject the production of a system the operation of which will cause theminimum interference in a receiver which is not tuned to thetransmission.

Hitherto in wireless transmission systems it has been the practice tomodulate the amplitude of a carrier oscillation in accordance with thesignal to be transmitted, and this results in the production of sidebands. Objectionable interference'is often caused by these side bands ina receiver not tuned to the transmission. According to this invention adouble transmission is simultaneously effected, that is to say .twocarrier oscillations of the same frequency but having a phasedisplacement relatively to one another are simultaneously modulated bythe signals which it is desired to transmit, and these two transmissionsare simultaneously received by a receiver tuned to the transmission.Subject to certain relations between the two carrier oscillations andthe modulations of those carriers hereinafter more particularlydescribed, the side bands of the transmission are ineffective at theirown frequencies due to the opposition of the side bands of one carrieroscillation to the side bands of the other carrier oscillation.

In order that the invention shall be more clearly understood, one formof transmission will be more particularly described with reference tothe accompanying drawing, it being of course understood that theinvention is not limited to the particular arrangement and apparatusdescribed.

In the drawing, Fig. 1 is a circuit diagram of a Wireless transmitteraccording to the invention,

Fig. 2 is a circuit diagram of a receiver adapted for use with thetransmission according to this invention and Figs. 3 and 4 are vectordiagrams illustrative of the present invention.

Referring to Fig. 1, an oscillation generator I adapted to generateoscillations of a desired carrier frequency is coupled by a transformer2 to the grid circuits of two transmitter valves 3 and 4 arranged inpush-pull relation. The anodes of the valves 3 and 4 are connectedthrough condensers l and 8 respectively to separate transmittingantennae 9 and Ill. The anodes of valves 3 and 4 are also connectedthrough tuned circuits 5 and 6 to the anodes of two modulator valves I3and I4, the latter anodes being also connected through choke coils IIand I2 respectively to the positive terminal of a source of high tension(not shown), the negative terminal of which is earthed. The gridcircuits of the modulator valves I3 and M are connected to the ends ofthe secondary winding of a transformer I5 the centre point of which isearthed through a suitable grid bias battery IS. A microphone I1 iscoupled through an amplifier indicated by l8 t0 the primary Winding ofthe transformer I5. A suitable biasing battery I9 is also provided forthe valves 3 and i and the negative terminal of this battery isconnected through a resistance 10 29 to the grid of the valve 3 andthrough a condenser 2I to the grid of the valve 4. Either or both of theelements 20 and 2| may be variable and by adjusting their relativevalues the phase difierence between the carrier oscillations in 15 tunedcircuits 5 and 6 can be adjusted. The phase diiference may be made aboutand. should preferably not exceed this.

The signal voltages from the microphone I! which are fed to the grids ofvalves I3 and I4 will clearly be phase displaced relatively to oneanother. The amplitudes of the signal oscillations in the anode circuitsof the valves I3 and I4 should preferably be made substantially exactlyequal and opposite and this can be done by adjusting the rheostats 22and 23 which are arranged in the filament heating circuits of thevalves. A suitable source of filament current is connected to terminals24.

The nature of the signals transmitted by the circuit of Fig. 1 will bestbe understood by reference to Figs. 3 and 4. The two carriers which are90 phase displaced relatively to one another, when unmodulated, arerepresented by vectors A and B in full lines. When they are modulated,the vector A reaches value 0 when vector B reaches value D and vector Ais at E when B is at F. Assuming that the modulation causes the vectorsA and B to vary between C and E and D and F respectively, the resultantenergy transmitted from both aerials will vary between the position G,through position H corresponding to zero modulation to position J. Itwill be noted that the resultant vector always lies between parallels Kand L.

The resultant vector can be resolved into two components, one a vector Hof constant length and direction and the other a vector M varyingbetween the full line value through zero length to the dotted linevalue. The only variable component thus remains in the line L andproduces no net effect upon a receiver of ordinary type.

A manner in which such a transmission can be received will beappreciated from an inspection of Fig. 4, where like vectors have thesame references as in Fig. 3. If there were combined with the receivedsignal a vector such as N, this vector N would have a component Pneutralizing vector H and a component Q making the variations of M allin one sense, namely to the right in the figure. Even if the vectorcomponent Q were shorter than shown it would introduce sufficientasymmetry for the signals to be heard but it would operate lesseificiently.

The receiver shown in Fig. 2 isadapted. to do this. A tuned circuit 25is connected between the receiving antennae 26 and earth and thiscircuit is tuned to the incoming carrier frequency. The" circuit isconnected through :a condenser 2'l shunted by a grid leak 28 to thegridcircuit of a thermionic valve 29 acting as a detector. The anode circuitof the valve 29 is coup-leda-bya transformer 39 to a low frequencyamplifyingvalve 3| which is coupled through a transformeru32. to aloudspeaker 33. The anode of valve 29 is connectednthrough a condenser.34 .to the grid of a phase changingvalve 35,.a resistance 36 beingconnected between the gridsand .cathode of this valve. may be variable.Theanode circuit of the valve 35 contains a coil 37 variably coupled tothe tuned circuit 25. A source of'voltage 38 is provided for the threevalves29', 3| and35.

a The'circuiti'fromthe tuned ci'rcuit25 through :valve29, transformer30, valve 3|, transformer 32 to'zloudspeakeni-iSin a conventionalreceiving circuit. In addition to this, however, there is the valve 35and itsassociated circuits. By adjusting the condenser. or'resistance'SB, or both, the phaseoiztheoscillations fed back by coil 31 canbei'adjusted. f If, for example, the phase'is made suchthatitheoscillation fedby coil'3l into circuit 25 are represented by thevector R in Fig. 4, then' these retroactive oscillations twill tend todrag :the original oscillations; represented by vectOra'I-I, intostep'with them. Any tendency for vectorI-Ito rotate to the right willmake R move to the rightahso. Finally the vector R will tend to take upa-position N in which the vector H is balanced out. The modulations thenbecome audiblesin the -;loudspeaker 33.

*Inany case it will'be observed that so long as thevector R-has acomponent in the direction Q (Fig. 4), that is to say so long asthe-vector R.- is phase displaced relatively to vector H-by an angleother than 180, itscomponent in'the direction Eithenor both of theelements 34 and 3E Q will make the varying vector M asymmetrical and somake the signals audible. The most efficient condition is, however, thatin which the vector added is as shown at N.

I claim:

1. A transmission system comprising means for generating two carrieroscillations of the same frequency but displaced in phase relatively toone another, a source of electricalvariations corresponding tointelligenceto be transmitted, means for deriving from said variationstwo sets of elec- 3 itrical variations of like wave form but phasedisplaced relatively to one another, means for ami plitude'modulatingone of said carrier oscillations with oneof-saicl sets of variations andfor simultaneously amplitude modulating the other of saidcarrieroscillationsawith the other of said sets of variations and tunedradiating means for sepa- I can'ieroscillations.

3i=A transmission system-comprising means for generating two.carriercscillations of the same frequency but displaced in: phase bysubstantially" relatively to oneanother, a source of electricalvariaitionscorresponding to intelligence to be transmitted, meansforderiving from said variations twoirsets .of electrical variations oflike wave? form but phase displaced by substantially relatively to oneanother, means for amplitude; modulating :one of saidcarriersosc'illations withone of said sets of variations and forsimultaneously amplitude modulating the other of said carrieroscillations with the other. of said sets of variationszandtunedradiating means for. separately transmitting-said carrier oscillations.

1 .GEORGE WILLIAM WALTON.

